<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <style>
        #camera{
            float: left;
            margin: 20px;
        }
        #contentHolder{
            width: 300px;
            height: 300px;
            margin-bottom: 10px;
        }
        #btn_snap{
            margin: 0 auto;
            border: 1px solid #f0f0f0;
            background: #5CACEE;
            color: #FFF;
            width: 100px;
            height: 36px;
            line-height: 36px;
            border-radius: 8px;
            text-align: center;
            cursor: pointer;
            cursor: pointer;
            /*禁止选择*/
            -webkit-touch-callout: none; /* iOS Safari */
            -webkit-user-select: none; /* Chrome/Safari/Opera */
            -khtml-user-select: none; /* Konqueror */
            -moz-user-select: none; /* Firefox */
            -ms-user-select: none; /* Internet Explorer/Edge */
            user-select: none; /* Non-prefixed version, currently not supported by any browser */
        }
        #imgBoxxx{
            width: 200px;
            margin: 60px 20px 20px;
        }
    </style>

</head>
<body>

<div id="camera">
    <div id="contentHolder">
        <video id="video" width="300" height="300" autoplay></video>
        <canvas style="display:none;" id="canvas" width="300" height="300"></canvas>
    </div>
    <div id="btn_snap">拍照</div>
</div>

<script>
    var canvas = document.getElementById("canvas"),
        pzBtn = document.getElementById("btn_snap"),
        context = canvas.getContext("2d"),
        video = document.getElementById("video");
    alert('该页面会调用您的摄像头')
    // 旧版本浏览器可能根本不支持mediaDevices，我们首先设置一个空对象
    if (navigator.mediaDevices === undefined) {
        navigator.mediaDevices = {};
    }
    // 一些浏览器实现了部分mediaDevices，我们不能只分配一个对象
    // 使用getUserMedia，因为它会覆盖现有的属性。
    // 这里，如果缺少getUserMedia属性，就添加它。
    if (navigator.mediaDevices.getUserMedia === undefined) {
        navigator.mediaDevices.getUserMedia = function (constraints) {
            // 首先获取现存的getUserMedia(如果存在)
            var getUserMedia = navigator.webkitGetUserMedia || navigator.mozGetUserMedia;
            // 有些浏览器不支持，会返回错误信息
            // 保持接口一致
            if (!getUserMedia) {
                return Promise.reject(new Error('getUserMedia is not implemented in this browser'));
            }
            //否则，使用Promise将调用包装到旧的navigator.getUserMedia
            return new Promise(function (resolve, reject) {
                getUserMedia.call(navigator, constraints, resolve, reject);
            });
        }
    }
    var constraints = { audio: false, video: {width: 720,height:720} }
    navigator.mediaDevices.getUserMedia(constraints)
        .then(function (stream) {
            var video = document.querySelector('video');
            // 旧的浏览器可能没有srcObject
            if ("srcObject" in video) {
                video.srcObject = stream;
            } else {
                //避免在新的浏览器中使用它，因为它正在被弃用。
                video.src = window.URL.createObjectURL(stream);
            }
            video.onloadedmetadata = function (e) {
                video.play();
            };
        })
        .catch(function (err) {
            console.log(err.name + ": " + err.message);
        });



    pzBtn.addEventListener("click", function () {
        // 点击，canvas画图
        context.drawImage(video, 0, 0, 300, 300);
        // 获取图片base64链接
        var image = canvas.toDataURL('image/png');
        // 定义一个img
        var img = new Image();
        //设置属性和src
        img.id = "imgBoxxx";
        img.src = image;
        //将图片添加到页面中
        document.body.appendChild(img);

        // base64转文件
        function dataURLtoFile(dataurl, filename) {
            var arr = dataurl.split(','), mime = arr[0].match(/:(.*?);/)[1],
                bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);
            while (n--) {
                u8arr[n] = bstr.charCodeAt(n);
            }
            return new File([u8arr], filename, {type: mime});
        }
        console.log(image);
        console.log(dataURLtoFile(image, 'aa.png'));
    });
</script>

</body>
</html>